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This Simple Explanation Tells You How Propane Fuel is Made

How is Propane Fuel Made?
Propane plays an important role as an energy source. It has several domestic and industrial applications. We find out what it is, and how it can be extracted from various sources.
Satyajeet Vispute
Last Updated: Jun 3, 2018
Did You Know?
Propane gas is odorless and colorless. It is also highly flammable. Therefore an external odorant is added to it for easy detection in case of a leak.
Whenever a liquid boils, it's our natural tendency to assume that it must be very hot. However, there is one liquid which boils at temperatures much below the freezing point of water. But that's not all that is amazing about it. Believe it or not, this liquid which boils at freezing subzero temperatures, also produces a gas that burns! Bewildering isn't it? This unusual liquid is known as propane.

Propane is one of the many by-products obtained from petroleum. But being a by-product doesn't mean that it's a waste product. It finds a lot of use in everyday life. As a matter of fact, propane on being turned into energy by burning, satisfies nearly 4% of the energy requirements of the U.S.

Propane is a useful handyman in many homes. It cooks the food in our kitchens, heats the water in our bathrooms and even warms our house when it's cold. In the farms, it allows the farmer to generate electricity, warm his chicks and fuel his tractors.

Propane finds use in industries as well. It is used to power that workhorse of large factories―the forklift truck. It is also used for heat treating different metals and for a myriad of other industrial uses.

Clearly, therefore, propane is an important source of energy. In the following sections, we shall look at what this bizarre yet highly useful fuel is, and how is it made.
What Elements is Propane Made Of
Propane is an alkane comprising a linear chain of 3 carbon atoms. Its molecular formula is C3H8. It belongs to the group of liquefied petroleum gases which includes butane, propylene, butadiene, butylene, isobutylene, and its mixtures.

Propane is a gas at room temperatures, but becomes a liquid under high pressure or low temperatures. It has a molecular weight of 44.1 g/mol and has a boiling point temperature of -43.6ºF at 1 atm.
How is Propane Made
Propane is a naturally occurring gas which gets created along with several other hydrocarbons, such as crude oil, gasoline, and butane, from the decomposition of organic matter beneath the Earth's surface over a long period of time. It is usually found as a mixture in natural gas and oil reserves and has to be processed in order to be separated. The following are the two main ways of extracting propane from its natural reserves.

Both methods begin with the digging of oil wells to pump out the oil that is present underground. The oil and gas mixture that is pumped out of the oil well is collected into a gas trap. The crude oil in the mixture being heavier, sinks to the bottom of the trap and is pumped out for further refinement. The 'wet' gas from the mixture rises to the top of the trap from where it is piped out for processing. Propane is extracted from both these natural sources as discussed below.

From Natural Gas

The natural gas used by consumers is very different from the 'wet' gas that comes out of the wells. It is almost purely methane, while that present in the wells comprises several different constituents, such as methane, hydrocarbons, moisture, hydrogen sulfide, helium, nitrogen and other compounds, that make it impure. For the purpose of purification, natural gas is processed, and it is during this processing that propane is obtained from it as a by-product.

Natural gas processing involves separating all the different hydrocarbons and fluids from the raw gas in order to obtain pure pipeline quality dry gas. Propane is extracted from these fluid components as a by-product. To separate propane, hydrocarbons are fractionated by passing the raw natural gas through an oil. The oil which is used has an affinity for hydrocarbons and readily absorbs them. The hydrocarbons from the hydrocarbon-rich oil are later separated on being adsorbed by surface-active agents or through the process of refrigeration.

Natural gas typically consists of nearly 90% methane and only 5% propane. Yet, half of the propane used in the U.S., is derived from natural gas.

From Oil

During the process of refining crude oil, liquefied petroleum gases are produced at various stages. The liquefied petroleum gases have two major components―propane and butane―which together constitute a total of 1% to 4% of processed crude oil.

To separate propane from it, crude oil is made to undergo the process of fractional distillation. In this stage, heavier hydrocarbons present in the oil sink to the bottom, whereas lighter ones, including propane, are easily extracted from the uppermost layer of the mixture.

The quantity of propane obtained using the oil extraction is usually variable and depends on the particular type of oil refinery.

Propane burns much more cleanly as compared to other fuels such as gasoline, kerosene etc. It releases much fewer harmful emissions including greenhouse gases, and is therefore, a much better alternative fuel especially for powering vehicles. But propane reserves are only as extensive as those of oil and natural gas. And with the tremendous increase in the demands for fossil fuels in the past few decades, it is quite likely that the natural stores of propane, along with all the other fossil fuels, will run out in the near future.

In response to this, scientists have begun investigating alternative sources of energy. In many laboratories across the world, fuels are being artificially produced. Propane has been chosen as the best candidate for being artificially created, thanks to its lower emissions and ease of transport. The following are the two artificial means of production of propane that are currently being researched.

From Biomass

Many renewable sources including vegetable oil and biomass, such as sugarcane, switchgrass, etc., are being considered for synthesizing propane. Scientists have successfully been able to demonstrate the production of propane from these sources in laboratories; however, the procedures being used currently aren't very cost-effective. A lot of research is being done in order to find an economical way of producing propane from these sources.

From Bacteria (E. coli)

Recently, a team of scientists from London have successfully demonstrated that they can obtain propane from glucose by using a genetically engineered version of the bacterium E. coli. Basically, the team was able to modify the process of fatty acid synthesis in this bacterium by introducing a group of enzymes into it that eventually resulted into the conversion of fatty acids to propane.
How is Liquid Propane Made from Propane Gas
Propane gas when liquefied, compresses to nearly 270 times its volume as a gas. This makes it possible to transport a large amount of propane making liquefaction of propane of great commercial importance. Propane gas is liquefied using high pressure or by freezing it to very low temperatures.

Propane needs to be carefully isolated from the mixture of petrochemicals. If these impurities are allowed to remain, propane won't liquefy properly. Appropriate temperatures and pressures are critical for optimum liquefaction. For this, standards and specifications have been established by the liquefied gas industry.

Commercially useful propane cannot have more than 0.0017 ounces (0.05 ml) of residual matter and must have a maximum vapor pressure of 200 psig at 100º F. Other than this, commercial propane also needs to adhere to the standards for corrosiveness, volatility, moisture, etc.
Thus, propane is derived using different processes from its natural sources such as natural gas and oil. Research is also being carried out for producing it artificially. Propane as a fuel can act as an almost clean source of energy. Produced artificially and in a renewable manner, it may even help solve our energy crisis in the coming years.